An optical proximity sensor detects the presence of a nearby object (the presence of reflection of emitted light by an object) by emitting infrared light from a light emitting device toward the outside of a set in which the optical proximity sensor installed and detecting reflected light returned from outside of the set by a light receiving device.
In this connection, many techniques have been conventionally proposed and disclosed.
Incidentally, a measure against crosstalk is very important to the optical proximity sensor in order to enhance its accuracy of detection.
FIG. 7 is a schematic view illustrating a conventional proximity sensor. Referring to this figure, a proximity sensor 300 is configured as a module including a substrate 310, a light emitting device 320, a light receiving device 330, a case member 340 and light condensing members 350 and 360. The light emitting device 320 is a light emitting diode. The light receiving device 330 has a single light receiving part 331 as a means for detecting light incident from the outside of a set (i.e., light reflected from an object).
Crosstalk occurring in the proximity sensor 300 may be caused by (1) reflected light Lx returned from a top surface 410 of an opening window 400, (2) reflected light Ly returned from a bottom surface of the opening window 400, and (3) leaked light Lz transmitted inside the module.
The crosstalk due to the reflected light Lx can be reduced substantially to zero by adjusting a gap d31 between the proximity sensor 300 and the opening window 400. However, in order to correctly detect the proximity of an object in which infrared light does not reflect off of well (such as a black hair), it may be difficult to reduce the crosstalk to zero.
The crosstalk due to the reflected light Ly can also be reduced substantially to zero by adjusting the gap d31.
The crosstalk due to the leaked light Lz can be reduced substantially to zero by a module design (such as thickening of a light shielding wall member 341, or adjustment of a distance d32 between light emitting and light receiving by the light emitting device 320 and the light receiving device 330).
A measure against the above-described conventional crosstalk has basically been achieved by adjusting the gap d31 between the proximity sensor 300 and the opening window 400.
FIGS. 8 to 10 are schematic views illustrating variations (first to third examples) of a gap adjusting method, respectively.
In the first example of FIG. 8, gap adjustment is achieved by installing an interposer (pedestal) 600 between the proximity sensor 300 and a printed circuit board 500. The proximity sensor 300 and the printed circuit board 500 are electrically interconnected through a via (not shown) formed inside the interposer 600.
In the second example of FIG. 9, gap adjustment is achieved by bending a flexible circuit board 700 on which the proximity sensor 300 is mounted, and interposing a thick member 800 (such as sponge rubber).
In the second example of FIG. 10, gap adjustment is achieved by installing a thick member 900 (such as sponge rubber) on the top surface of the proximity sensor 300. The thick member 900 has openings 910 and 920 formed respectively to correspond to light condensing members 350 and 360 of the proximity sensor 300. The second example (FIG. 9) and the third example (FIG. 10) may be used in combination.
According to the above-described conventional gas adjusting methods, since the gap d31 can be arbitrarily adjusted, it is possible to reduce crosstalk due to the reflected lights Lx and Ly.
However, the gap adjusting methods of the second example (FIG. 9) and the third example (FIG. 10) have problems in that deviation of the gap d31 and a wobble of the thick members 800 and 900 are likely to occur and the effect of reduction of the crosstalk becomes unstable.
In addition, in the above-described conventional gap adjusting methods, separate gap adjusting members 600, 800 and 900 in addition to the proximity sensor 300 are required and a plurality of gap adjusting members 600, 800 and 900 having an optimized thickness for different sets having different specifications should be prepared, so that there are problems in that work burden increases and the cost of the entire set increases.